Nanomaterials are at the heart of many new technologies, and they are projected to become even more important. Their unique behavior gives them certain advantages (and disadvantages) over traditional, macroscale materials. Through some clever analysis, researchers are finding out more about how hydrogen is uniquely absorbed in palladium nanoparticles, a process which may have important implications for advanced energy applications.
The palladium-hydrogen system is a classic. Palladium absorbs hydrogen readily, even at room temperature. For this reason, it has been thoroughly studied in regard to hydrogen storage and fuel cell applications (in addition to catalysis and others). A research team at Stanford has taken it a step further as they’ve studied how individual nanocubes of palladium absorb hydrogen in real time
The difficulty of such a task is that nanoparticles are often studied with transmission electron microscopy (TEM). Electron microscopy requires high vacuum to achieve suitable resolution. To expose palladium to hydrogen at elevated pressures would ruin the vacuum. Using a special, environmental TEM, the palladium nanocubes could be imaged while varying the hydrogen.
As described in a Stanford News article, the way the hydrogen is absorbed is unexpected. As the hydrogen pressure is increased, it reaches a point where the H2 molecules dissociate to elemental hydrogen and enter the palladium lattice. The transition is abrupt when the hydrogen is absorbed or desorbed. It is very much an all-or-nothing process.
The way the hydrogen is absorbed is useful for its “binary” characteristics in addition to other properties. The hydrogen is absorbed at lower pressure and the nanoscale particles can withstand cycling better than macroscale counterparts. The absorption of hydrogen results in a volumetric expansion of about 10% which can damage bulk sections.
This work is expected to lead into research on other nanoscale shapes such as spheres and rods, as well as guide work on alternative materials. Although palladium has characteristics which make an ideal research material, it also has drawbacks limiting its suitability. With a density about the same as lead, it’s too heavy to be an efficient storage material. It’s not cheap either. It does, however, provide valuable insight into nanoscale absorption phenomena which may enable more efficient storage options.
Photo courtesy of Stanford News and Dionne Group